A Typical Scenario: A Clean-Looking House Where Everyone Falls Ill in Turn

This example case is a composite of situations that commonly follow floods; it is not a review from any specific customer. Nid's family lives in a two-storey townhouse in a housing estate in Pathum Thani. Knee-deep water sat on the ground floor for several days, so the whole family moved upstairs and used one bedroom as a dining room, a playroom and a storeroom at the same time.

When the water receded, Nid and her husband shovelled out the mud, hosed the floors and wiped the walls with a scented floor cleaner. The house looked almost normal. Two days later, their three-year-old began vomiting and had loose stools. The next day Grandma, who is over seventy, had diarrhoea too, while their older child developed a cough, a mild fever and a sore throat. Nid took everyone to a doctor, who explained that several viruses can cause these symptoms and stressed safe drinking water, handwashing and preventing spread at home.

What Nid had never considered was that the bathroom door handle, the stair rail, the TV remote, the edge of the dining table and the plastic toys rescued from the water were the easiest places for a virus to pass from one person to the next, especially once someone was already ill. Looking clean and being disinfected are two different steps.

The 2026 Floods and the Risk from Viruses After Floods

According to a Daily News report citing Thailand's Department of Disaster Prevention and Mitigation (DDPM) at 06:00 on 5 October 2026, floods affected 26 provinces plus Bangkok, a total of 1,270,151 households. Many families crowd together, share bathrooms or move to shelters. These are exactly the conditions viruses favour, because viruses spread from person to person. The closer people live and the more they share, the easier it is for an infection to travel.

The World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) agree that floodwater should always be treated as contaminated with sewage and germs, and that surfaces touched by floodwater should be cleaned first and then disinfected. Thailand's Department of Disease Control also warns every rainy season about diarrhoeal disease, food- and water-borne illness, respiratory infections and conjunctivitis, many of which are caused by viruses.

How We Ranked Viruses After Floods (Editorial, Not Official)

This is an editorial ranking by the WHD team for public education. It is not an official ranking by any health authority and it is not calculated from this year's case data. We combined five criteria:

1. How often it appears in flood guidance from WHO, CDC and the Department of Disease Control, such as diarrhoeal, respiratory and eye infections.
2. How easily it spreads through water, food, hands, droplets and shared surfaces.
3. How persistent it is in the environment, judged qualitatively only. For example, non-enveloped viruses are generally hardier than enveloped ones.
4. Severity and who is at risk, with extra weight for young children, older adults, pregnant women and people with weak immunity.
5. Relevance to surfaces at home, meaning how much cleaning and surface disinfection can reduce the risk.

The order therefore reflects what is most useful to know for homes and buildings after a flood. For local outbreak information, follow your provincial health office and the Department of Disease Control.

Why Viruses Deserve Their Own Ranking

Unlike mold or some bacteria, viruses cannot grow on a floor by themselves. They need to get inside human or animal cells to multiply. That does not make a virus on a surface harmless: many viruses remain infectious for a while after leaving a sick person, and someone who touches that surface and then touches their mouth, nose or eyes can pick them up.

Scientists broadly split viruses into two groups. Enveloped viruses, such as influenza, RSV and SARS-CoV-2, have a fatty outer layer that soap and common disinfectants break down fairly easily. Non-enveloped viruses, such as norovirus, rotavirus, hepatitis A, adenovirus and enteroviruses, lack that layer and are generally more resistant to the environment and to many cleaning products.

Viruses After Floods Ranked: The Top 10 to Know Before You Move Back In

No. 1: Norovirus, the Fastest-Spreading Stomach Virus at Home

Why it ranks first: Norovirus is a leading cause of acute gastroenteritis worldwide. It spreads through water, food, hands and surfaces, a very small dose can make someone ill, and it is non-enveloped, so it is fairly hardy. Combined with damaged bathrooms and crowded living after a flood, it is the first virus to guard against.

Where it hides: bathroom floors, toilet seats, taps, door handles, kitchen sinks, chopping boards, hand towels and anywhere someone has vomited, since droplets from vomiting can travel further than you can see.

Symptoms and who is at risk: nausea, vomiting, watery diarrhoea, stomach cramps and sometimes a low fever. It usually comes on quickly and passes, but young children and older adults can become dehydrated. Seek medical care if someone passes little urine, becomes drowsy or is very weak.

Prevention: wash hands with soap and clean water after using the toilet and before preparing food, give a sick person a separate bathroom if possible, throw away food that touched floodwater, and wear gloves when cleaning up vomit or faeces.

Cleaning and spraying: norovirus is among the organisms the CHEMGENE HLD4H product information lists as covered (according to product information). Spraying after visible dirt has been removed helps reduce it on bathroom, kitchen and shared surfaces more evenly than spot wiping.

No. 2: Rotavirus, a Threat to Young Children

Why it ranks here: rotavirus is a major cause of severe diarrhoea in young children. It spreads by the faecal-oral route and is a non-enveloped virus with reasonable environmental persistence. When floodwater brings sewage indoors and toddlers put things in their mouths, the risk rises.

Where it hides: plastic toys, crawling mats, living room floors, pram seats, changing tables, and bottles or feeding equipment rinsed in unsafe water.

Symptoms and who is at risk: vomiting, frequent watery stools and fever. Babies and toddlers can dehydrate quickly; watch for fewer wet nappies, a dry mouth, crying without tears or unusual sleepiness, and see a doctor promptly. Ask your doctor about rotavirus vaccination.

Prevention: use boiled or bottled water for formula, wash hands after nappy changes, discard soft toys that soaked up water, and keep play areas apart from rooms not yet cleaned.

Cleaning and spraying: rotavirus is not named on WHD's pages, so we make no tested claim for it. It belongs to the virus group the product says it covers, and WHO and CDC advise cleaning and then disinfecting flood-contaminated surfaces. Ask the WHD team for test data on rotavirus if you need it.

No. 3: Hepatitis A Virus, from Contaminated Water and Food

Why it ranks here: hepatitis A spreads through water and food contaminated with faeces and is one of the illnesses health agencies routinely warn about when water and sanitation systems are disrupted. It is non-enveloped and known to be hardy, and its long incubation period means people may spread it before they realise they are ill.

Where it hides: unsafe water sources, drinking-water containers that were submerged, produce washed in dirty water, and kitchen surfaces exposed to sewage.

Symptoms and who is at risk: tiredness, loss of appetite, nausea, stomach pain, yellow skin or eyes, and dark urine. Children may have mild symptoms; adults and people with existing liver disease need particular care. See a doctor if you suspect it, and ask whether vaccination is suitable for you.

Prevention: drink safe water, cook food thoroughly, never eat food or vegetables that were under water, and wash hands before eating or cooking.

Cleaning and spraying: hepatitis A is not named on WHD's pages and is known for its resilience, so we make no kill claim. Focus first on thorough cleaning, then use surface spraying as an added step, and ask WHD for organism-specific test data if you want details.

No. 4: Enteroviruses, the Cause of Hand, Foot and Mouth Disease

Why it ranks here: several enteroviruses, including coxsackieviruses and enterovirus 71, cause hand, foot and mouth disease, which is common in young children during the rainy season. It spreads through saliva, nasal mucus, blister fluid and faeces, so when children from several households share a shelter or a relative's house, transmission becomes easier.

Where it hides: shared toys, spoons, bowls, cups, cot rails and floor play areas.

Symptoms and who is at risk: fever, sore mouth and mouth ulcers, and a rash or blisters on palms and soles; children may eat less because their mouth hurts. A small number become seriously unwell. If a child is very drowsy, vomits repeatedly, breathes fast or has unusual jerking movements, go to hospital at once.

Prevention: keep sick children home, separate their personal items, wash hands often, clean toys frequently and avoid sharing cups.

Cleaning and spraying: the hand, foot and mouth virus is listed on WHD's service page (according to service information). Spraying children's rooms, living areas and water-safe toys after cleaning helps limit its spread at home.

No. 5: Adenovirus, Behind Pink Eye, Diarrhoea and Colds

Why it ranks here: adenoviruses cause conjunctivitis, sore throats, colds and diarrhoea in children. Conjunctivitis is something the Department of Disease Control often warns about during floods, because people wash their faces in unclean water and rub their eyes with contaminated hands. Adenoviruses are non-enveloped and fairly persistent.

Where it hides: shared face cloths and towels, pillowcases, door handles, light switches and washbasins.

Symptoms and who is at risk: red, irritated, watery eyes with discharge, sore throat, cough or loose stools. Children and crowded households are most exposed. See a doctor if the eye is very painful, vision blurs, or it does not improve.

Prevention: never share towels, wash your face with clean water, avoid rubbing your eyes, and launder bedding in clean water and dry it fully in the sun.

Cleaning and spraying: adenovirus is not named on WHD's pages; it belongs to the virus group the product says it covers. Clean first, then spray shared touch points, and request test data for this organism if needed.

Viruses After Floods Ranked 6 to 10: Respiratory and Environmental Viruses

No. 6: Influenza, Including H1N1

Why it ranks here: floods usually coincide with the rainy season, when influenza is common in Thailand. Wading through water, getting soaked, sleeping badly and sharing enclosed rooms all make infection and onward spread easier. Influenza is enveloped and less hardy than the stomach viruses, but its severity for older adults and people with chronic illness earns it this place.

Where it hides: droplets from coughs and sneezes that settle on tables, rails, phones, remotes, cups and shared blankets.

Symptoms and who is at risk: sudden high fever, body aches, headache, cough, sore throat and exhaustion. Older adults, young children, pregnant women and people with diabetes, heart or lung disease should see a doctor; anyone short of breath needs urgent care. Ask your doctor about flu vaccination.

Prevention: wear a mask when ill or caring for someone ill, cover coughs, wash hands, open windows and let sick people rest in a well-ventilated room.

Cleaning and spraying: H1N1 and H5N1 influenza are listed on WHD's service page (according to service information). Spraying shared touch points after cleaning reduces residual virus on surfaces, alongside ventilation and personal hygiene.

No. 7: Respiratory Syncytial Virus (RSV)

Why it ranks here: RSV circulates widely in the rainy season and is a major cause of lower respiratory infection in babies and toddlers. Adults may only have a cold, yet carry it to children at home. It spreads through droplets and through touching surfaces and then the face.

Where it hides: cot edges, toys, mattresses, blankets, bottles, teats and adults' hands.

Symptoms and who is at risk: runny nose, cough and fever; babies may breathe fast, wheeze or feed poorly. Premature babies, children with heart or lung conditions and older adults need close watching. Seek care at once if a child struggles to breathe.

Prevention: wash hands before holding a baby, wear a mask if you have a cold, avoid kissing babies' faces, and clean toys that go into mouths.

Cleaning and spraying: RSV is listed on WHD's service page (according to service information). Spraying children's rooms and touch points after cleaning helps, and toys that go into mouths should be rinsed with clean water afterwards as the technicians advise.

No. 8: SARS-CoV-2 (COVID-19) and Other Coronaviruses

Why it ranks here: COVID-19 does not arrive with floodwater, but post-flood life means crowded rooms, shared bathrooms and poor rest, all of which favour respiratory viruses. It still circulates, and older adults and people with chronic illness remain at higher risk.

Where it hides: shared dining tables, stair rails, door handles, lift buttons and common areas where volunteers and neighbours come and go.

Symptoms and who is at risk: fever, cough, sore throat, runny nose, fatigue and sometimes loss of taste or smell. Anyone with breathing difficulty should see a doctor straight away.

Prevention: test when symptomatic, isolate when ill, mask in crowded spaces and keep air moving.

Cleaning and spraying: SARS-CoV-2 and human coronavirus 229E are listed in WHD's product and service information. The CHEMGENE HLD4H product page states 99.85% against COVID-19 within one minute, and the service page states 99.99% germ elimination (according to product and service information).

No. 9: Hepatitis E Virus

Why it ranks here: WHO notes that hepatitis E spreads mainly through drinking water contaminated with faeces, especially where water and sanitation are disrupted. It ranks ninth because its main route is drinking water rather than household surfaces.

Where it hides: untreated water, storage tanks that floodwater entered, submerged water dispensers and poorly washed containers.

Symptoms and who is at risk: similar to other forms of hepatitis: tiredness, poor appetite, yellow skin or eyes. Pregnant women and people with liver disease should take particular care and see a doctor if symptoms appear.

Prevention: drink bottled or boiled water, clean and disinfect water tanks before reuse following local guidance, and do not use a flooded dispenser until it has been checked.

Cleaning and spraying: hepatitis E is not named on WHD's pages. Surface spraying does not make drinking water safe, but it helps reduce contamination on kitchen and water-storage surfaces after washing. Ask WHD if you want organism-specific data.

No. 10: Dengue Virus, Carried by Mosquitoes After the Water Recedes

Why it ranks here: dengue does not spread through surfaces or floodwater. After floods, however, water collects in containers, tyres, plant saucers and debris, creating breeding sites for Aedes mosquitoes. It sits last here not because it is mild, but because surface disinfection is simply not the tool for it, and we want that to be clear.

Where it hides: standing water around the house, uncovered tanks, plant saucers, blocked gutters and washed-in rubbish.

Symptoms and who is at risk: several days of high fever, headache, pain behind the eyes, muscle pain and sometimes small red spots. The period when the fever drops needs close watching; abdominal pain, repeated vomiting, drowsiness or bleeding require hospital care immediately.

Prevention: empty or cover containers, clear rubbish, use repellent, sleep under nets and join community clean-ups as advised by the Department of Disease Control.

Cleaning and spraying: WHD's service disinfects surfaces; it is not a mosquito or larvae control service. Remove standing water and contact local authorities for mosquito fogging.

Why Soap or Bleach Alone May Fall Short

Soap lifts mud and grease that shelter germs, but it does not reliably inactivate every virus, especially non-enveloped ones left in grooves and corners. Bleach is often mixed at the wrong strength, poured onto muddy floors, or combined with toilet cleaners to form harmful gases, and it corrodes metal and fades fabrics. Scented floor cleaners are not designed for a house soaked in sewage, and hand wiping misses walls and high spots.

WHD Post-Flood Disinfection Spraying with CHEMGENE HLD4H

According to service information, trained WHD technicians spray and/or ULV-fog (Ultra Low Volume fine mist) CHEMGENE HLD4H, a medical-grade UK disinfectant containing benzalkonium chloride and didecyldimethylammonium chloride. WHD's pages describe it as broad-spectrum against viruses, bacteria and fungi, listing SARS-CoV-2, human coronavirus 229E, RSV, H1N1, H5N1, HIV, norovirus, hand, foot and mouth virus, vaccinia virus, mycobacteria, Salmonella and Bordetella pertussis, with 99.99% stated on the service page. Listed endorsements include the Department of Medical Sciences, Mahidol University, NHS England and EN 14476:2013+A2:2019. For viruses not named there, such as rotavirus, hepatitis A and E and adenovirus, we make no tested claim; ask WHD for data.

Spraying comes after mud removal and washing. People and pets leave the zone during application and return at the time the technicians give, typically about 30 minutes according to service information. We do not claim there is no residue, and anyone who is ill should see a doctor.

1. Book and survey: call 065-556-6294 or LINE @whd268 with the area, flood depth and any illness at home.
2. Remove mud and wash: discard soaked items and dry the house.
3. Zone and prepare: food, dishes and personal items are covered; people and pets leave.
4. Spray: with extra attention to handles, rails, switches, bathrooms and play areas.
5. Re-enter: after the advised time, ventilate, and rinse food-contact items and mouthed toys.

10 Reasons to Book Spraying When Viruses Worry You

1. Norovirus spreads via surfaces, and the disinfection service uses a product that lists it.
2. Spray reaches walls, corners and spots hands miss.
3. It helps stop illness passing around the household.
4. It suits homes with crawling, mouthing toddlers.
5. It protects older adults and people with chronic illness.
6. Trained technicians know the priority spots and wear proper protection.
7. No risky home mixing of chemicals.
8. Short wait, about 30 minutes per service information.
9. Works for homes, condos, shops, schools and offices; see the service page.
10. Peace of mind that every step, from washing to disinfecting, is done.

Before and After

Example case: after the doctor's care, Nid's family discarded soaked toys, re-washed the bathrooms and kitchen, dried the house for two days, then booked WHD. Technicians sprayed three zones while the family waited across the road, then advised rinsing dishes and plastic toys before use.

Checklist

• Before: check electrics, wear boots, gloves and a mask, wash, discard flooded food and soft toys, clean water tanks, dry the house.
• After: re-enter on time, ventilate, rinse mouthed items, wash hands, use separate towels, empty standing water, watch for symptoms.

FAQ

Is this ranking official? No, it is WHD's editorial ranking based on the five criteria above.

How long do viruses last on surfaces? It depends on the virus, surface and conditions; non-enveloped viruses are generally hardier. We give no fixed figure.

Someone has diarrhoea. When should we spray? See a doctor first, then book a time when everyone can leave the zone, and tell technicians which rooms the patient used.

Does spraying prevent dengue? No. Remove standing water and prevent bites.

Does it kill rotavirus or hepatitis A? They are not named on WHD's pages, so we make no tested claim; ask WHD for data.

House Washed? Let WHD Finish the Job

Book Post-Flood Disinfection Spraying

Call 065-556-6294 | LINE @whd268

Related Services and References

• WHD Disinfection Spraying Service
• Residential Ozone Disinfection for musty homes
• Daily News, DDPM flood update, 06:00 5 Oct 2026: dailynews.co.th/news/6249374
• WHO fact sheets: who.int; CDC Floods: cdc.gov/floods; Department of Disease Control: ddc.moph.go.th